Image processing apparatus and image processing system using the apparatus

ABSTRACT

An image processing apparatus is composed of a plurality of function processing units for performing image processing, a high priority function selection part for selecting functions, execution of each of which is required by a corresponding one of the function processing units, based on the predetermined priority for each of the functions; and a data control unit including a data transfer part for preferentially accessing the shared memory which the function selected by the high priority function selection part requires, and a plurality of data holding parts, each of the data holding parts holding a predetermined amount of data transmitted with each of the plurality of function processing units, wherein the data transfer part controls the bus connecting the CPU and the shared memory based on requirement sent from each of the function processing units, and each of the plurality of function processing units transmits data with the data control unit separately from the others of the plurality of function processing units, and executes its function in parallel to the others of the plurality of function processing units.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an image processing apparatus processing a plurality of functions, and especially to an image processing apparatus and an image processing system using the apparatus in which a plurality of functions are efficiently executed by using a shared memory as both a main memory for a CPU and an image memory.

[0002] As a first example of a conventional image processing technique for processing an image at a high speed, for example, as disclosed in Japanese Patent Application Laid-Open Hei 5-307531, the composition of an image processing apparatus with a plurality of image memories exclusively used for an image processing unit is shown in FIG. 2A. In this image processing apparatus, the feeding of data to be processed from one of the image memories to the image processing unit can be performed in parallel to storing the processed data to the image memory, which can improve the speed in image data processing. Also, even if the image processing unit is substituted with an image input/output unit, it is possible to access the image memory in parallel while simultaneously performing an image input task and an image output task. That is, reading image data out of the image memory can be performed in parallel to writing in image data into the image data.

[0003] Moreover, as a second example of a conventional image processing technique for processing an image at a high speed, for example, as disclosed in Japanese Patent Application Laid-Open Hei 5-120239, the composition of an image processing apparatus with a shared memory provided for a CPU as a main memory and for an image processing unit as an image memory is shown in FIG. 2B. In this image processing apparatus, since the shared memory is used by the CPU, the image processing unit, and the image input/output unit, it is possible to reduce the amount of hardware parts, which can downsize an image processing system. If both the image processing unit and the image input/output unit includes a part capable of controlling a bus, the scope of operations performed by the image processing unit and the image input/output unit can be easily expanded by connecting the part to the bus.

[0004] However, in the first conventional example shown in FIG. 2A, since the image processing apparatus includes a plurality of image memories in order to process an image at a high speed, there is a large amount of hardware. Moreover, since it is necessary to indirectly accesses data in the image memory via the image processing unit when the CPU accesses data in the image memory, overhead is required to perform the access. This overhead makes it difficult to realize high-speed access to the image memory from the CPU. On the other hand, in the second conventional example shown in FIG. 2B, since the CPU, the image processing unit, and the image input/output unit all use the shared memory, there is a problem in that the load of the bus 2 shown in FIG. 2B becomes heavy. For example, if calculational processing of image data and input/output processing of picture data are executed in parallel, since the access to the image data and the picture data in the shared memory is performed via the bus 2, the load of the bus 2 is heavier than that in an image processing apparatus with an image memory exclusively used for image processing. That is, in the composition of the second conventional example, since the arbitration of the bus 2 is necessary, the overhead required for the arbitration of the bus 2 makes it difficult to increase the processing speed of the image processing apparatus when both the image processing unit and the image input/output unit frequently use the bus 2.

[0005] Furthermore, since the second conventional example shown in FIG. 2B does not possess a plurality of buses for the image processing unit and the image input/output unit to exclusively perform their respective access, various sets of image data cannot be processed in parallel. For example, feeding image data out of the shared memory to the image processing unit cannot be performed in parallel to sending the processed image data from the image processing unit to the shared memory. Accordingly, the processing speed is decreased in the second conventional example.

SUMMARY OF THE INVENTION

[0006] The present invention has been achieved in consideration of the above-described problems, and is aimed at providing an image processing apparatus in which a plurality of image processing functions is processed in parallel by realizing a method of efficient memory access, and the image processing can consequently be executed at a high speed.

[0007] To attain the above object, the present invention provides an image processing apparatus in which the main memory of a CPU is used as a shared memory, also functioning as an image memory, and image processing is performed by a plurality of function processing units, the image processing apparatus comprising:

[0008] a high priority function selection part for selecting functions, with the execution of each being required by a corresponding one of the function processing units, based on a predetermined priority for each of the functions; and

[0009] a data control unit including a data transfer part for preferentially accessing the shared memory, as required by the function selected by the high priority function selection part, and a plurality of data holding parts provided between the shared memory and the plurality of function processing units, with each of the plurality of data holding parts holding a predetermined amount of data which is processed by a corresponding one of the plurality of function processing units;

[0010] wherein each of the plurality of function processing units transmits with the data control unit separately from the others of the plurality of function processing units, and executes its function in parallel to the others of the plurality of function processing units. !!

[0011] Moreover, in the above image processing apparatus, the data control unit is connected to the CPU and the shared memory via a bus, and the data transfer part controls the bus connecting the CPU and the shared memory based on requirement for data transfer requested by each of the function processing units.

[0012] Furthermore, in the above image processing apparatus, each of the data holding parts includes a bit-width change function for changing both the bit-width of data transferred in the bus connecting the CPU and the shared memory and the bit-width of data processed by the function processing units, and transmits data with the bus in synchronization with the same operation clock as the clocks used for the bus, and data with the function processing units in synchronization with the same operation clock as the clocks used for the function processing units.

[0013] Additionally, in the above image processing apparatus, the data control unit simultaneously accesses image data of a plurality of pixels, stored in the shared memory, the number of the plurality of the image data corresponding to the bit-width of data stored in the shared memory.

[0014] Also, in the above image processing apparatus, the data transfer part reads multiple types of image data out of the shared memory by turns and sends the multiple types of image data to the plurality of data holding parts, and each of the plurality of data holding parts stores the image data sent to the data holding part and transmits image data with one of the function processing units independent of the others of the function processing units, the one being connected to the data holding part and executing image processing in parallel to the others of the function processing units.

[0015] Further, in the above image processing apparatus, sending of resultant data obtained by processing in each of the function processing units to a corresponding one of the data holding parts is performed in parallel to the inputting of the stored image data to the function processing unit from the one of the data holding parts.

[0016] Further still, in the above image processing apparatus, the data control unit and the plurality of function processing units are integrated in an integrated circuit formed in one silicon chip.

[0017] On the top of that, the present invention provides an image processing system in which a main memory of a CPU is used as a shared memory that is also used as an image memory, the image processing system comprising:

[0018] an image processor including a plurality of function processing units for performing image processing, a high priority function selection part for selecting functions, execution of each of which is required by a corresponding one of the function processing units, based on a predetermined priority for each of the functions; and a data control unit including a data transfer part for preferentially accessing the shared memory which the function selected by the high priority function selection part requires, and a plurality of data holding parts provided between the shared memory and the plurality of function processing units, each of the plurality of data holding parts holding a predetermined amount of data which are processed by a corresponding one of the plurality of function processing units, in which each of the plurality of function processing units transmits with the data control unit separately from the others of the plurality of function processing units, and executes its function in parallel to the others of the plurality of function processing units;

[0019] an image input unit connected to the image processor, to input data of an image;

[0020] wherein the shared memory stores image data input from the image input unit;

[0021] an image output unit connected to the image processor, to output data of an image obtained by processing in the image processor; and

[0022] buses for connecting the image processor, the CPU, and the shared memory.

[0023] In accordance with the present invention, it is possible to reduce the load of a bus connecting a main memory of a CPU and a plurality of function processing units used for image processing, by providing a plurality of data holding parts provided between the shared memory and the plurality of function processing units. Furthermore, since each of the plurality of data holding parts holds a predetermined amount of data which are to be processed by a corresponding one of the plurality of function processing units, each of the plurality of function processing units can execute its function in parallel to functions executed by the others of the function processing units.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic block diagram showing the concept of an image processing apparatus of an embodiment according to the present invention.

[0025]FIGS. 2A and 2B are diagrams showing examples of conventional image processing apparatuses.

[0026]FIG. 3 is a more detailed composition of the image processing apparatus shown in FIG. 1.

[0027]FIGS. 4A and 4B are diagrams for explaining the pixel data storage method in a shared memory provided in the image processing apparatus of the embodiment.

[0028]FIG. 5 is a timing chart showing operations of the image processing apparatus of the embodiment.

[0029]FIG. 6 is a block diagram showing the composition of a data control unit of the embodiment.

[0030]FIG. 7 is a flow chart showing operations of a data transfer function of the embodiment.

[0031]FIG. 8 is a block diagram showing operations of memory access to control parts in the data transfer part of the embodiment.

[0032]FIGS. 9A, 9B, and 9C are diagrams showing examples of the data bit-width changing method used in the embodiment.

[0033]FIG. 10 is a diagram showing another example of the data bit-width changing method used in the embodiment.

[0034]FIG. 11 is a timing chart for explaining the priority processing performed in the embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] Hereafter, details of the embodiments will be explained with reference to the drawings.

[0036]FIG. 1 is a schematic block diagram showing the concept of an image processing apparatus of an embodiment according to the present invention. By using FIG. 1, the principle of the image processing performed in this embodiment is outlined below.

[0037] The CPU 1 controls the whole of the image processing apparatus. Control programs executed by the CPU 1 and data used for the control programs are stored in a shared memory 2. The data used for the control programs, such as image data to be processed, parameters for filtering of image data, and so on are stored in the shared memory 2. The CPU 1 controls the image processing apparatus while accessing the shared memory 2 and reading out necessary data or writing in resultant data. Image processing functions such as an arithmetic operation, image pick-up and display functions, etc., are performed by a function processing unit 5, a function processing unit 7, and so on, respectively and separately. When the function processing units 5 and 7 execute their functions, the units 5 and 7 send their respective execution demand signals to a high priority function selection part 30 separately via signal lines 6 and 8, and require access to the necessary image data in the shared memory 2. The high priority function selection part 30, which has received the execution demand signals sent from the function processing units 5 and 7, determines the execution order of the functions (the execution of which is demanded by each of the processing units 5 and 7) based on the predetermined priority order of the functions. Moreover, the high priority function selection part 30 sends a signal for executing the function having the highest priority to the data transfer part 20. The data transfer part 20 accesses the shared memory 2 so that the function selected by the high priority function selection part 30 can be processed, and then reads a set of image data out of the shared memory 2, sets of image data obtained by the memory access are held in data holding parts 40 and 41, respectively, and are further sent to the function processing units 5 and 7. Here, the data control unit 4 includes the data transfer part 20, the high priority function selection part 30, and the data holding parts 40 and 41.

[0038] According to the above-mentioned principle of the embodiment of the present invention, each of the data holding parts 40 and 41 stores the data processed by a corresponding one of the function processing units 5 and 7. Therefore, if each of the processing units 5 and 7 processes data within the amount of data stored in each data holding part, the function processing units 5 and 7 can execute their functions in parallel. Thus, efficient data storage becomes possible by using the data holding parts 40 and 41, which can improve the processing speed of the image processing apparatus.

[0039]FIG. 3 is a more detailed composition of the image processing apparatus shown in FIG. 1.

[0040] In the following, the embodiment shown in FIG. 3 will be explained in detail.

[0041] The image processing apparatus shown in FIG. 3 includes an image input unit 60 for controlling the input operation for image data picked-up by an image pickup device, an image output unit 70 for controlling the output operation which outputs image data to an image display device such as a monitor, and image processing units 80 and 90, each possessing a plurality of image processing functions. Image data to be processed are input to the image input unit 60 from an image pickup device such as a camera. Image processing operations such as a pixel conversion operation, an arithmetic operation, an edge enhancement operation, a feature extraction operation, a template matching operation, and so on are executed in the image processing units 80 and 90 by using image data stored in the shared memory 2. Each function of the image processing units 80 and 90 is controlled by the CPU 1 via a function control unit 50. Here, the arbitration of the bus 3 is not carried out by the image input unit 60, the image output unit 70, or the image processing units 80 and 90, but only by the CPU 1 and the data control unit 4. Accordingly, in this embodiment according to the present invention, since the load of the arbitration of the bus 3 is reduced, it is possible to improve the processing speed of the image processing apparatus. In addition, since the image processing units, and the image input and output units are connected in parallel to the data control unit 4 controlling the bus 3, the image processing operations controlled by the data control unit 4 can be executed in parallel. Furthermore, although the processor 10 is composed of the function control unit 50, the data control unit 4, and the image processing units 80 and 90 in this embodiment as shown in FIG. 3, it is also possible that the processor 10 includes the image input and output units 60 and 70.

[0042] A method of storing the pixel data (that is, image data) in the shared memory 2 provided in the image processing apparatus is explained in detail below with reference to FIGS. 4A and 4B.

[0043] In this embodiment of the present invention, the bit-width of an image data signal is eight bits. Therefore, in the following expansion, the bit-width (depth) of image data input from the image input unit 60 and image data fed to the image processing units 80 and 90 is assumed to be eight bits.

[0044] First, a matrix of a logical data arrangement for pixel data—that is, image data—used for the image processing, is shown in FIG. 4A. Next, f(x, y) in this figure indicates the value of an individual pixel data at the coordinates (x, y). Now, in the following, it will be explained how the image data shown in FIG. 4A are stored in the shared memory 2. In this embodiment, the bit-width of data stored in the shared memory 2 is 32 bits. Therefore, image data of four pixels are stored together at one address in the shared memory 2. Accordingly, in this embodiment, it is possible to access image data of four pixels within one cycle of a clock for the bus 3. Consequently, the data transfer speed of the bus 3 becomes four times that of the data processing speed of image processing in which image data of only one pixel is processed in one cycle of the clock for the function processing units. Thus, in this embodiment, by making use of this feature, image data are efficiently transferred from the shared memory 2 to the data holding parts 40 and 41. Moreover, the priority of each function is preset to the high priority function selection part 30 as follows.

[0045] That is, the priority of the image input processing function>that of the image output processing function>that of the image processing function.

[0046] Although this priority order is changeable as a matter of course, each function should be given its priority in advance.

[0047] In the following, the image processing operations performed in this embodiment are explained in detail with reference to FIG. 3-FIG. 6.

[0048] Here, The method of executing the additive arithmetic operation of two images A and B for image data allotted to their address in the shared memory 2 as shown in FIG. 4B is explained. Also, this additive arithmetic operation is performed by the image processing unit 80.

[0049] An outline of operations executed by the image processing unit 80 is described as follows when the additive arithmetic operation is performed.

[0050] To begin with, the CPU 1 sends an instruction signal and parameters necessary for the execution of the additive arithmetic operation to the image processing unit 80 via the function control unit 50. Meanwhile, the additive and subtractive arithmetic operations executed by the image processing unit 80 are switched according to parameters set in a register provided in the image processing unit 80. After sending the parameters, when two sets of image data a and b of images A and B are fed via signal lines 83 and 84, respectively, the image processing unit 80 executes the additive arithmetic operation of the images A and B, and outputs the resultant image data r obtained by the additive arithmetic operation to a signal line 85. In the transferring of the sets of the image data a and b, a validity signal for the transferred image data a and b is also sent to the image processing unit 80 together with the image data a and b. The image processing unit 80 processes only image data which the validity signal indicates to be valid. According to this embodiment, since the image data a and b are fed in parallel, and the image processing unit 80 also outputs the resultant image data r in parallel to the feeding of the data a and b, the image processing can be efficiently executed. The above-explained operations are shown in the timing chart in FIG. 5. Details of this timing chart will be explained later.

[0051] Furthermore, the feeding of the two sets of the image data a and b is explained in detail below.

[0052] The CPU 1 sets the parameters necessary to feed the image data a and b and store the resultant image data r obtained by the arithmetic operation to the data transfer part 20 via a signal line 51. That is, the set parameters are parameters to designate addresses in the shared memory 2, at which the image data a and b are stored, the amount of the image data to be processed by the additive arithmetic operation, and parameters to designate addresses of the shared memory 2, at which the resultant image data r are stored. After the setting of the above parameters for access to the shared memory 2, the CPU 1 sets the status of the image processing unit 80 such that the unit 80 starts execution of the additive arithmetic operation of the images A and B. The setting of the status is carried out by setting the status of bits in a status register of the image processing unit 80. The image processing unit 80 sends a data demand signal requiring the transmission of image data used for executing the additive arithmetic operation to the high priority function selection part 30 shown in FIG. 6 via a signal line 82. The high priority function selection part 30 turns on a bit of a function-demand register (not shown in FIG. 6) in the high priority function selection part 30, corresponding to the demand signal sent from the image processing unit 80, and controls access to the shared memory so that the access to data required by each of functions for which bits of the function-demand register are turned on is performed in the priority order of these functions. Here, it is also possible to adopt another priority processing method in the high priority function selection part 30, in which when the high priority function selection part 30 receives an demand signal requiring data, sent from one of the image processing units, the part 30 checks for the presence of demand signals from other image processing units, and if demand signals from other image processing units exist, a comparison among priority values of functions executed in the other image processing units sending the demand signals is carried out by the part 30, and memory access is performed based on the result of the comparison. For example, if demand signals requiring data are sent from image processing units other than the image processing unit 80, there is a check to examine whether or not priority values of functions executed by the other image processing units are higher than that of the function executed by the image processing unit 80. Further, if the priority of the image processing unit 80 is higher than that of each of the other image processing units, or there is only the demand signal from the image processing unit 80, the high priority function selection part 30 permits the data transfer part 20 to access the shared memory 2 to acquire the data required from the image processing unit 80 via the signal line 31. Afterward, the image data a in the shared memory 2 is accessed, and the read-out image data a are temporarily stored in the data holding part C 120. Also, the image data b in the shared memory 2 is accessed, and the read-out image data a are also temporarily stored in the data holding part D 130. After the transfer of the image data a and b from the shared memory 2 to the respective data holding parts C 120 and D 130 is completed, the image data a and b are fed to the image processing unit 80 from the data holding parts C 120 and D 130, respectively. Furthermore, the resultant data r obtained by the operations in the image processing unit 80 are output when the predetermined number of cycles has passed after the completion of the data feeding for the image data a and b, and are stored in the data holding part E 140. Finally, the resultant data r are stored in the shared memory 2.

[0053] The above-explained operations are shown on the timing chart in FIG. 5. As shown in FIG. 5, the image data a0-a39 and the image data b0-b39 are divided into two sets, and the two sets are transferred by two separate transfer operations. The reason why the image data a and b are transferred by two separate transfer operations is that it is assumed that the capacity of the data hold pats C 120 and D 130 is 20 bytes each. The operations shown on the timing chart in FIG. 5 are controlled by the data transfer part 20 according to the flow chart shown in FIG. 7. In this embodiment, the image data are transferred to the data holding parts C 120 and D 130 via the bus 3 by making use of the full transfer ability of the bus 3. Therefore, the transfer of the image data a and b occupies a period (the shortest period which is determined by the amount of the transferred image data and the transfer ability of the bus 3) shorter than the time necessary for the image processing unit 80's processing of the image data a and b. Accordingly, since it becomes possible for other image processing units such as the image input/output unit to use the bus 3 while the bus 3 is open, the processing speed of the image processing apparatus can be increased. Although the bus 3 is occupied for a period while accessing image data required by one of the image processing units, the bus 3 is also left open to the image processing units for a preset period. Therefore, if the access and the transfer of the image data required by the image processing unit are completed, and the preset period has not expired yet, another image processing unit can require access to necessary image data in the shared memory 2 without new arbitration to obtain the occupation right for the bus 3. The arbitration of the occupation right for the bus 3 is carried out by a bus arbitration part (not shown in this figure) in the data control unit 4.

[0054] In FIG. 5, the timing control for the image output processing is also shown. As shown in FIG. 5, the period of the operation clock CLK3 used for the image input/output processing is set at a longer cycle than that of the operation clock CLK1 used for the data access and transfer in the bus 3, and that of the operation clock CLK2 used for processing in the image processing units. It is because the frequency in the operation clock for the image input and output devices is as low as 12.5 MHz or 25 MHz. However, in this embodiment, since image data used for the image outputting operation are transferred to the data holding part B 110 by using the full transfer ability of the bus 3, it is possible to minimize the occupation period of the bus 3.

[0055] In the above embodiment, the capacity for the data holding parts C 120, D 130, and E 140 is a comparatively small number of bytes. It is because these data holding parts possess only enough capacity to absorb the difference between the data transfer ability of the bus 3 and the data processing ability of the processing unit 80. In this embodiment, the data transfer ability of the bus 3 is higher than the data processing ability of the processing unit 80, and it is not necessary to provide large capacity data holding parts to make the most of the full transfer ability of the bus 3.

[0056] As a mater of course, although the capacity of the data holding parts C 120, D 130, and E 140 is 20 bytes each, it is possible to increases the capacity to more than 20 bytes.

[0057] Also, although the data holding parts C 120, D 130, and E 140 are provided in the data control unit 4, it is possible to provide these data holding parts in the image input unit 60, the image output unit 70, the image processing unit 80, or the image processing unit 90.

[0058] Meanwhile, in the above embodiment, the operation clock CLK2 signals are not sent to the image processing unit 80 for the intervals other than the period in which valid data are transferred or the validity signal is sent. This control of CLK2 is carried out to reduce the consumption power in the image processing apparatus.

[0059] In the following, details of the data transfer part 20 will be explained with reference to FIG. 8. Three sets of parameters (address region, the number of image data to be processed, and so on) necessary for processing the image data a and b, and the resultant data r are set to the memory access control parts C 220, D 230, and E 240, respectively. The setting of these parameters to the memory access control parts C 220, D 230, and E 240 is performed by the CPU 1 via a signal line 53. The information on data required by the function selected by the high priority function selection part 30, that is, a signal including the set of parameters for the function whose requirement for access to image data necessary for its processing is allowed, is sent to a bus-interface processing part 21, and the part 21 executes the allowed memory access.

[0060] For example, when the access to the image data a is carried out, operations of the bus-interface processing part 21 are performed as follows.

[0061] To begin with, the bus-interface processing part 21 obtains the occupation right for the bus 3, and informs the memory access control part C 220 of that the usage right for the bus 3 has been obtained. And further, the memory access control part C 220 generates a signal (at least including the addresses of the required image data a, and the number of the image data a) necessary for access to the shared memory, and reads the image data a out of the shared memory 2. The image data a read out of the memory 2 are stored in the data holding part C 120 via a signal line 121.

[0062] According to this embodiment, the function processing units do not need to obtain the occupation right for the bus 3 while the bus-interface processing unit 21 maintains the occupation right for the bus 3. For example, after the image data a are acquired, the image data b can be acquired without arbitration of the bus 3. Moreover, in another example, even if an interruption is required for image input during the arithmetic operation, the bus-interface processing part 21 does not obtain the occupation right for the bus 3 (the arbitration of the bus 3). As mentioned above, it becomes possible to efficiently use the bus 3 and improve the processing speed of the image processing apparatus by reducing the frequency of the arbitration of the bus 3. This embodiment is especially effective if the capacity of the respective data holding parts A 100-F 150 is small, or if interruptions are frequently required for high priority processing functions.

[0063] In this embodiment, the bit-width for data stored in the shared memory 2, data transferred in the bus 3, and data stored in the data holding parts A 100-F 150 is 32 bits. On the other hand, that for data input to or output from the image input unit 60, the image output unit 70, and the image processing units 80 and 90 is 8 bits. Control of the data-width for processed data is explained below with reference to FIGS. 9A-9C and FIG. 10.

[0064] The transfer of data from the shared memory 2 to the data holding parts A 100-F 150 is carried out with a bit-width of 32 bits to make the best of the transfer ability of the bus 3. With regard to FIGS. 9A-9C, the data transfer for the data holding part C 120 is explained below. In the first example, as shown in FIG. 9A, the data transferred via a signal line 121 are stored in the data holding part C 120 with a bit-width of 32 bits. The operation clock used for the bus 3 and data transfer is CLK1. On the other hand, if data are input to the image processing unit 80 via a signal line 83, data with a bit-width of 8 bits, which the image processing unit 80 can process, are serially input to the unit 80 by using the operation clock CLK2 which is also used for the unit 80. Here, a pixel data is expressed in 8 bits.

[0065] In the above-explained control of the bit-width, which is shown in FIG. 9A, all the data read-out of the shared memory 2 are used for image processing. However, in some cases, it is not necessary to use all the data stored in each data holding part. For example, as shown in FIG. 9B, if the image processing is executed using the data-contraction with a ratio of ½, only a half of the data stored in one of the data holding parts is input to the image processing unit 80. Also, as shown in FIG. 9C, if the image processing is executed using the data-contraction with a ratio of ⅛, the amount of data which is accessed in the shared memory 2 is reduced to by one half, and the same control of the bit-width as that shown in FIG. 9B is performed. The -control of the above access to the shared memory 2 can be realized by adding a circuit for controlling access to the shared memory 2 to the memory access control part C 220. As mentioned above, any ratio of the data contraction can be attained by controlling both the amount of data which is accessed in the shared memory 2, and the data transferred from the corresponding data holding parts.

[0066] Next, the input of data sent from the image input unit 60, the image processing unit 80, and so on to the data holding part A 100, the data holding part E 140, and soon is explained below with reference to FIG. 10.

[0067] The image data are input in synchronization with the same operation clock CLK3 as the clock used for the image input unit 60, and the holding of the image data is performed at the time when the signal for storing data shown in FIG. 10 is turned on. Further, the image data are transferred to the shared memory 2 in synchronization with the same operation clock CLK1 as the clock used for the bus 3.

[0068] Operations of the high priority function selection part 30, in which the performance of another process is required during the period in which image processing is being performed, are explained below. In these operations, as shown in FIG. 11, an interruption to perform a function with a higher priority executed in the image output unit 70 is required during the performance of a function executed in the image processing unit 80. If the performance of a function with a higher priority than the priority of the performed function in the image processing part 80 is required, the access to the shared memory 3 for the function performed in the image processing unit 80 is immediately interrupted. And further, the execution state of the image processing unit 80 at the time when the performance of the function is interrupted is stored in the memory access control part C 210, and after the access to the shared memory 2 for the higher priority function which required the interruption is completed, the access to the memory 2 for the interrupted function in the image processing unit 20 is restarted.

[0069] According the embodiments of the present invention, it is possible to transfer data by making the most of the transfer ability of the bus 3 in any operational state when the image processing units use the bus 3. Furthermore, since each function for image processing can be performed without receiving the effects of the other functions, and independent of the state of the bus 3 if the data necessary for the function exist in a corresponding data holding part, it is possible to improve the processing speed of the image processing apparatus.

[0070] In the above embodiments according to the present invention, a function performed in a function processing unit can be implemented by one or more physical means, or a plurality of functions performed in one or more function processing can be implemented by one physical means.

[0071] Moreover, according to the present invention, it becomes possible to execute image processing functions performed in an image processing apparatus in parallel by providing a data holding part for each image processing function.

[0072] Furthermore, according to the present invention, even if the processing speed of the image processing is lower than the speed of the data transfer in a bus connecting a CPU and its main memory, it is possible to efficiently use the bus by making the most of the transfer ability of the bus, which improves the processing speed of an image processing apparatus.

[0073] Thus, in accordance with the present invention, by providing data holding parts between a group of image processing units executing image processing functions and a shared memory used as both a main memory of a CPU and an image data memory, it becomes possible to reduce the load of a bus connecting the CPU and the shared memory. 

What is claimed is:
 1. An image processing apparatus in which a main memory of a CPU is used as a shared memory that is also used as an image memory, and image processing is performed by a plurality of function processing units, said image processing apparatus comprising: a high priority function selection part for selecting functions, execution of each of which is required by a corresponding one of said function processing units, based on a predetermined priority for each of said functions; and a data control unit including a data transfer part for preferentially accessing said shared memory which said function selected by said high priority function selection part requires, and a plurality of data holding parts provided between said shared memory and said plurality of function processing units, each of said plurality of data holding parts holding a predetermined amount of data which are processed by a corresponding one of said plurality of function processing units; wherein each of said plurality of function processing units transmits with said data control unit separately from the others of said plurality of function processing units, and executes its function in parallel to the others of said plurality of function processing units.
 2. An image processing apparatus according to claim 1, wherein said data control unit is connected to said CPU and said shared memory via a bus, and said data transfer part controls said bus connecting said CPU and said shared memory based on requirement for data transfer requested by each of said function processing units.
 3. An image processing apparatus according to claim 2, wherein each of said data holding parts includes a bit-width change function for changing both the bit-width of data transferred in said bus connecting said CPU and said shared memory and the bit-width of data processed by said function processing units, and transmits data with said bus in synchronization with the same operation clock as the clocks used for said bus, and data with said function processing units in synchronization with the same operation clock as the clocks used for said function processing units.
 4. An image processing apparatus according to claim 3, wherein said data control unit simultaneously performs memory access to image data of a plurality of pixels, stored in said shared memory, the number of said plurality of said image data corresponding to said bit-width of data stored in said shared memory.
 5. An image processing apparatus according to claim 2, wherein said data transfer part reads multiple types of image data out of said shared memory by turns and sends said multiple types of image data to said plurality of data holding parts, and each of said plurality of data holding parts stores said image data sent to said data holding part and transmits image data with one of said function processing units independent of the others of said function processing units, said one being connected to said data holding part and executing image processing in parallel to the others of said function processing units.
 6. An image processing apparatus according to claim 5, wherein sending of resultant data obtained by processing in each of said function processing units to a corresponding one of said data holding parts is performed in parallel to said inputting of said stored image data to said function processing unit from said one of said data holding parts.
 7. An image processing apparatus according to claim 5, wherein said data control unit and said plurality of function processing units are integrated in an integrated circuit formed in one silicon chip.
 8. An image processing system in which a main memory of a CPU is used as a shared memory that is also used as an image memory, said image processing system comprising: an image processor including a plurality of function processing units for performing image processing, a high priority function selection part for selecting functions, execution of each of which is required by a corresponding one of said function processing units, based on a predetermined priority for each of said functions; and a data control unit including a data transfer part for preferentially accessing said shared memory which said function selected by said high priority function selection part requires, and a plurality of data holding parts provided between said shared memory and said plurality of function processing units, each of said plurality of data holding parts holding a predetermined amount of data which are processed by a corresponding one of said plurality of function processing units, in which each of said plurality of function processing units transmits with said data control unit separately from the others of said plurality of function processing units, and executes its function in parallel to the others of said plurality of function processing units; an image input unit connected to said image processor, to input data of an image; wherein said shared memory stores image data input from said image input unit; an image output unit connected to said image processor, to output data of an image obtained by processing in said image processor; and buses for connecting said image processor, said CPU, and said shared memory. 